Simplify the following expression: $r = \dfrac{-4x}{3} - \dfrac{5x}{3}$
Explanation: Since the expressions have the same denominator we simply combine the numerators: $r = \dfrac{-4x - (5x)}{3}$ Combine like terms: $r = \dfrac{-9x}{3}$ Simplify by dividing numerator and denominator by 3: $r = \dfrac{-3x}{1}$ $r = -3x$